The invention relates to memory devices, and, in particular, to memory management of devices for computer systems and the like. It finds particular application in memory systems that use partially working memory circuits where defective rows, columns, bits or bytes in the main memory circuit are replaced by good rows, columns, bits or bytes from a supplementary store (usually called a substitute store). These memory systems may include the controlling means to disable a defective area when it is being accessed and enable a replacement area. This controlling means is referred to as a partial memory engine.
In the semiconductor industry, solid state memory devices are fabricated as dice on wafers of silicon, each die containing a memory array. These die are tested and those which can be made to work perfectly are packaged for use. The other die, those which contain one or more defective memory cells, are usually either discarded or used in some fault tolerant memory device.